Burner and coaxial flame rod assembly



Jan. 12, 1954 w. H. E BELToFT 2,665,749

BURNER AND COAXIAL FLAME ROD ASSEMBLY Filed Nov. 10, 1949 2 Sheet's-Shee'c 1 III/I 3nnentor WILLIAM H. EBELTOFT Gttotneg Jan. 12, 1954 w. H. EBELTOFT BURNER AND COAXIAL FLAME ROD ASSEMBLY 2 Sheets-Sheet 2 Filed NOV. 10, 1949 vvvvvvvvvvvvwvv Suventor WILLIAM H. EBE LTOFT Gttorneg Patented Jan. 12, 1954 BURNER ANDCOAXIAL-FLAME ROD ASSEMBLY William H. Ebeltoft, San -Francisco, Calif., as-

Signor to Minneapolis-Honeywell Regulator KCOIIIPaDYfMiDHGaIDOIiS, Minn., a corporation of 7 Delaware Application November 10, 1949,Scrial No.'126,592

3 Claims. 1

The present invention is concerned with a new andimproved "flame rodassembly used in the de tection of a name ina fuel burner. More particularly, "the present invention is concernedwith a semi-flexible "flame rod assembly of the type which is'readilyadaptable to any type of a burner installation.

With the introduction "of electronic flame de- 'tectors into the field df fuelburner-controls, particularly the type of detectors relying on the electrical conducting properties 'of flame, there has been an increasing demand fora universal type of flame -rod assembly that could readily be applied to any type of burner installation. This *universal type "of flame rod assembly must be ponstruct'edt'o give positive sensing of the pres- "ence of'a burnerfiame by insuring that the flame contacts two principal conductors 'of the assemb'ly on anai'e'a that is suflicient to make the associated electronic detector operate-to indicate posi- *tively thepresence or absence of a burner flame. This assembly must also be constructedto permit forming and bending'a'fter-the assemblyha's been fabricated so that where an existing burner inistallation is ''being modified for electronic 'flam'e "detection, it is possible to install "the flame rod assembly regardless of the type of burner construction.

It is therefore anob je'ct of the present inven- *tion to provide a new and improved flame rod assembly that may be bent after the assembly has been fabricated.

A 'furth'erobject of the present inventionis to provide a semi-flexible flame rodassembly of 'coaxial construction which will permit bending oi the assembly when it is installed.

Another object of the present invention is to provide a flame rod assembly having a hollow thin wall cylindrical tube with a'central conductor supported therein by a number of insulating spacer members, the latter of which are'main- 'tained in position by further means which will not inhibit the bending of the assembly 'wh'enbeing prepared for a particular "installation.

Still another object of the present invention is the provision of a flame rod assembly of the coaxial type which may readily be combined with a pilot burner assembly to sense the .pilot flame and be readily disposed for association with a main burner.

These and other objects of the present invention will be understood upon a consideration of the following specification, claims 'andth'e "figures of which:

Figure 1 represents one particular embodiment -o't th'e invention applied to 'a gas pilifit burner;

Figure 2 represents an end view of impact "assembly shown in Figure 1 takenalo'ng the line Iz, 2;

Figure 3 shows a further embodiment o'fjthe invention as it may be adapted Lfor use wane combination gas and oil burner unit;

Figure 4 shows the assembly as applied to a pilot flame assembly incorporating an ignition circuit as well as the pilot burner; and

Figure 5 shows an end view of Figured.

Referring to Figure 1, the numeral 1B "represents the burner assembly which is particularly adapted to the burning of gas. The'supply ofgas for the burner I0 flows through asuit'ableconduit ll. Directly controlling the flow of the .gas in conduit II is a solenoid valve l2 which is of the type which will open the fuel valve whenever an energizing current is applied to the solenoid therein. A thermostatic control device 13 may be used to indicate the need for operation of the burner 19 and this thermostatic control device operates through appropriate electrical circuits in a control device M, the latter of which ill energize the solenoid'valve l2 whenevei-thethrmostat I3 is calling for burner operation'ah'd "a predetermined condition exists at an associated pilot burner assembly I5.

Located on one end of the pilot assembly Tl'5 is an air mixer I? which serves to regulate the ratio of fuel, from the conduit [6, to the air, flowing through the port in the side of the mixer. The mixed air and gas is fed through the remaining portion of the conduit is of the assembly 15 and emits from the right end thereof where the same is used to maintain functioning a constant'burning pilot'flame 24. The pilot flame may beignited by any desired means, not shown.

For sensing the presence of a pilot name, the flame rod assembly 19 has been provided and may be seen to comprise a thin wall conduit 20 which is made of a heat resistant material such as stainless steel or Nichrome. This conduit 20 extends through a hole in the left hand portion of the pilot assembly and to the right beyond the nozzle of the assembly and is centrally mounted therein by the hole in the left hand portion er "the pilot assembly and by a further supporting "and mixing element 23, the latter of which is located .iust inside of the nozzle of the pilot assembly. Centrally mounted within the conduit "20 is a rod of relatively small diameter '2! 'oi' metal capable of withstanding very high temperatures, a suitable example being Inconel, which is an alloy consisting of 80% nickel and 20% chromium. This center rod 2| is supported by a plurality of insulators 22. The material for these insulators may be of any suitable type of ceramic which will withstand high temperature or may even be quartz. The diameter of these insulating spacers 22 is slightly less than the inside diameter of the conduit 20 so that when it is desired to bend the tube in any particular direction there will be no binding between the conduit 20 and the insulators 22 which would cause cracking and destruction of the insulators. Inasmuch as it is necessary that the insulators 22 remain in a relatively fixed position on the rod 2| within the conduit 20, it is necessary to provide some means for preventing movement thereof. This may be accomplished in several ways. One way is to crimp the rod 2| on either side of the insulators leaving sufficient room for the insulators to move a relatively small distance if the assembly is to be bent. In the preferred embodiment, as shown, the rod is bent slightly at 25 on either side of the insulators. To prevent axial movement of the rod and insulators the outer surface of the thin wall conduit 2|] may be crimped as is shown at 26. Again, this crimping must be put in such a manner that it will permit a small amount of axial movement of the insulators to prevent cracking in the event that it is desired to bend the device when it has been assembled.

It will be obvious that each of the insulators may be retained by crimping the conduit as at 26, in which case crimping of the rod 2| may be unnecessary.

A suitable cover 28 is placed over the end of the flame rod assembly l9 to prevent the entry of harmful objects into the internal portion of the assembly. The outer conduit 2| may be connected by a suitable ground conductor 3| to the control device 14 while the central conductor is connected by a suitable conductor 30 through the control device l4.

The control device l4 may be of the type disclosed in the Wilson Patent, 2,448,502, issued August 31, 1948. This Wilson control device discloses an electronic flame detector which utilizes the conducting characteristics of a flame and particularly the rectifying characteristics of a flame wherein the conductivity of the flame is greater in one direction than it is in the other. When there is a flame existing at the end of the pilot assembly l5 and it is intersecting the outer surface of the conduit 20 and the rod 24, the latter projecting over the burner In, there will be a current flow between the conductor 30 through the rod 2|, the pilot flame 24, the surface of the conduit 20 and the ground conductor 3| to the control device I 4. With the pilot flame 24 impinging upon both the conduit 28 and the rod 2| and with the thermostatic device l3 calling for operation of the burner H), the control device M will be operative to energize the solenoid valve l2 so that gas will flow to the burner 0 and will be ignited by the pilot flame 24.

It will be obvious that with the arrangement shown in Figure l, the flame rod assembly l9 may be extended in any desired manner over the burner ||l so as to intersect not only the pilot flame 24 but also a burner flame in the burner II]. It will also be obvious that with the present arrangement a burner flame is striking the outer surface of the conduit 20 from the ar a e nding from the end of the pilot assembly conduit l8 clear to the right end of the conduit 20 thus providing a good contacting surface for the flame.

Figure 2 shows an end view of the pilot assembly |5 looking along the section line 2-2. This figure shows primarily the spaced relation between the insulator 22 and the inner diameter of the conduit 20, which spacing permits the bending of the assembly without the breaking of the supporting insulators for the rod 2|. The figure also shows the mixer 23 as it supports the conduit 20.

Referring to Figure 3, the numeral 40 represents a combination burner assembly which may use either gas or oil. The blower portion of the apparatus supplies air to a blast tube 4|. At the exhaust end of the blast tube 4| is an oil nozzle 42 which may be used to project atomized oil into a combustion chamber where the oil is to be burned. The supply of fuel for the oil nozzle 42 is fed through a suitable supply conduit, not shown, and the flow is controlled therein by a suitable control valve, not shown.

Ignition of the oil may be accomplished by an ignition electrode 43 connected to a suitable ignition transformer, not shown. Also located within the tube 4| is a gas ring 44 which has ports on the downstream side of the air blast tube 4| so that the gas will be fed into the air stream and mixed for combustion purposes. The flow of gas to the ring 44 is through a supply conduit 45 with a solenoid valve 52 controlling this fuel flow. The igniting of the gas flame is by way of the pilot assembly 46 which comprises a pilot burner 41 with a coaxial flame rod assembly 48 projecting through the center thereof. An ignition electrode 49 is provided for igniting the pilot flame. The flow of fuel to the pilot burner is controlled by a solenoid valve 50 located in the conduit 5|.

A thermostatic device l3 may be used to indicate the need for operation of the burner 4|! and this thermostatic device may operate through an appropriate control device 55. This control device may also incorporate an electronic type of flame detector which depends for its operation upon the conductivity of a flame.

If the control device 55 is set to control the oil nozzle, and the thermostatic device I3 is calling for operation of the burner, a flame will appear at the end of the blast tube and will be conical in shape with the edges of the cone defined on the drawing by the lines 60 and 6|, the point of the cone appearing at the nozzle 42. If the control device 55 is set to control the flow of gas instead of oil, then, upon a call for burner operation, the solenoid valve 58 will be energized and gas will flow to the pilot burner 41 where it will be ignited by the ignition electrode 49.

The pilot flame will pass over the flame detection assembly 48 at its upper end and this will result in a pilot flame being detected. When this is detected, the main valve 52 will be energized and gas will pass to the gas ring in the tube 4|. As the mixed gas and air flows out of the end of the tube 4| it will be ignited and the main flame will be cylindrical in shape with the edges of the cylindrical flame being indicated by the lines 62-63.

It will be noted that the flame from the oil burner does not cover all the same space-covered by the gas flame next to the burner. There will be formed a space adjacent the burner which is triangular in shape, on a cross sectional view, and which is defined on its edges by the lines 6t, 63, and the end of the burner blast tube 41. Within that space it .is generally desirable to locate the flame sensing portion of the flame rod assembly as there will be no oil flame present to affect the flame rod assembly. It has been found to be desirable to keep the oil flame off of the flame rod because of the corrosive action of an oil flame. The flame rod is thus used to sense on'ly the pilot and main gas flame and not the oil flame, the latter of which may be sensed by photocell or other means, not shown. The desirability of the semi-flexible flame rod assembly is feadily apparent here as it permits the combination of the flame rod with the pilct assembly and the positioning or bending of the same rod into a position where it will be sub- J'ect'ed to the gas flames but not to the oil flame.

in Figures 4 and 5, there shown another arrangement utilizing the coaxial flame rod assembly of the present invention. In 'ceitain types "of burners it has been found desirable to incorporate the flame detection apparatus, the pilot burner and conduit therefor, and ignition electrode assembly within a single conduit. By utilizing the coaxial flame rod assembly it becomes readily possible to construct such an arrangement, as has been shown in Figures 4 and 5.

A main conduit 10 is provided for enclosing the entire pilot assembly. This assembly includes a gas air mixer H on the left end of the pilot conduit 12. The conduit 12 leads to a pilot burner 13. The pilot burner flame may be started by an ignition electrode which in turn forms the central conductor of a coaxial ignition assembly comprising a hollow cylindrical conduit 14 with a solid insulating spacer 8| separating the conduit from the electrode 15 and supporting the latter. Diametrically opposite the ignition assembly in the conduit 10 is the flame detection portion of the apparatus and this comprises a hollow cylindrical conduit 16 with a flame rod 11 centrally supported therein by a plurality of quartz beads 18. The beads 18 are retained in position by the crimping of the flame rod on either side of the quartz beads as at 19. The conduit 16 is crimped as at B2 to prevent axial movement of the beads within the conduit. The beads in this arrangement have rounded outer edges to permit easier flexing of the assembly without danger of cracking the same. A flame stabilizing plate 80 is fastened across the end of the pilot burner 13 and lies between the ignition assembly and flame detection assembly. The end of the conduit 16 extends beyond the pilot burner so that its outer surface will be subjected to the pilot flame. The flame rod ll extends beyond the end of the conduit 16 for a certain distance and then it is bent to be effectively in parallel with the pilot burner face so that it will be subjected to a pilot flame when it is present at the burner.

With the arrangement last shown, it can be seen that the pilot assembly is assembled into an extremely compact unit which includes all the necessary elements for controlling and checking the pilot flame. Further, as with the other uses for the present invention shown in Figures 1 and 3, the flame from the pilot burner is used to contact the grounded surface of the conduit and the flame rod. All of these assemblies elimi-' hate the need for cutting of an additional hole in the fire walls of the burner for positioning a flame electrode therein as has been necessary when using the flame electrodes presently available on s market. Further, all assemblies are sufllciently flexible that they may be bent after installed to position the same in the most advantageous manner (for flame detection. purposes.

While specific embodiments of the invention have been shownand described, it is to be'understood that it has been for illustrative purposes only and that many modifications will be readily obvious to those skilled in the art. Therefore, I intend to be limited solely by the scope of the appendedla'ims which I claim:

1. A fuel burner assembly comprising a main burner and a pilot burner, means mounting said pilot burner in igniting relation to said main burner, a conduit for feeding fuel to said main bur-her, aconduit for feeding fuel to said pilot burner said pilot burner supporting a pilot flame when fuel is supplied thereto and having an end portion adapted to direct the pilot flame into the combustion area of main burner to thereby ignite said main burner when fuel issues therefrom, a bendable flame rod assembly, means mounting said flame rod assembly within said pilot burner, said flame rod assembly extending through said pilot burner and conforming to the shape thereof, said flame rod assembly extending beyond said end portion into the combustion area of said main burner, said flame rod assembly comprising a hollow cylindrical member of heat resistant metal extending into the combustion area of said main burner, a plurality of spaced insulating members therein, and a rod of heat resistant metal centrally mounted within said hollow cylindrical member by said plurality of spaced insulators and extending beyond the end of said hollow member into the combustion area of said main burner, the space between said rod and said hollow member forming a flame gap adapted to be bridged by a pilot flame only if of sufficient magnitude to extend into the combustion area of said main burner, detecting means including a pair of terminals, said detecting means indicating the presence of a burner flame when a predetermined electrical circuit has been completed between said pair of terminals, and means connecting said hollow cylindrical member to one of said pair of terminals and said rod to the other of said terminals to complete said circuit only when a flame of sufficient magnitude to ignite said main burner is present at said pilot burner.

2. A pilot burner assembly comprising, a pilot burner having an end adapted to direct a flame into a combustion area when fuel is supplied thereto, a coaxial assembly comprising a hollow conduit of heat resistant metal, a plurality of spaced insulators, and a flame rod of heat resistant metal centrally mounted therein by said plurality of spaced insulators, said rod extending beyond one end of said conduit and forming a gap between said hollow conduit and said flame rod which is adapted to be bridged by a flame, and means mounting said coaxial assembly in fixed relation to said pilot burner with said one end of said conduit extending into the combustion area, said conduit being readily bendable along its entire length so that said and extending into the combustion area is adapted to be bent into any desired portion of the combustion area at the end of said pilot burner, said hollow conduit forming a flame shield for said flame rod so that said gap is bridged only when a pilot flame exists at the desired portion of the combustion area at the end of said pilot burner.

3. A burner assembly comprising, a pilot burner having a nozzle adapted to direct flame into a combustion area when fuel is supplied thereto, a main burner having a nozzle adapted to direct flame into a combustion area when fuel is supplied thereto, means mounting said pilot burner in igniting relationship to said main burner so that a portion of the flame of said pilot burner intersects the combustion area of said main burner, a bendable hollow thin wall conduit of heat resistant metal, means mounting said conduit in fixed relationship to said pilot burner, said conduit having one end extending into the combustion area of said pilot burner so that a flame from said pilot burner will wipe over the outer surface and said one end of said conduit, a bendable metallic heat resistant conductor, and a plurality of spacer insulating members mounting said conductor centrally within said conduit so that said conductor extends beyond said one end of said conductor, said conduit being crimped on its circumference at a plurality of positions to maintain said spacer members in a relatively fixed relation with respect to said conductor, said bend- References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,162,501 Draper June 13, 1939 2,173,539 Peters et al Sept. 19, 1939 2,285,326 Bergtholdt June 2, 1942 2,304,200 Plein et a1 Dec. 8, 1942 2,335,471 Ashcraft Nov. 30, 1943 2 396,146 Atwater Mar. 5, 1946 2,496,502 Steensma Feb. 7, 1950 

